(1) Field of the Invention
This invention relates to an improved process for the preparation of 2,2'-bis(4-substituted phenol)sulfides which are useful as light stabilizers, polyolefin modifiers, lubricating oil additives, and intermediates for the manufacture thereof. It also relates to 2,2'-bis(4-cumylphenol)sulfide, i.e. 2,2'-bis(4-.alpha.,.alpha.-dimethyl benzyl-phenol)monosulfide, which is a novel compound.
(2) Description of the Prior Art
Generally, 2,2'-bis(4-substituted phenol)sulfides are prepared by reaction of a corresponding 4-substituted phenol with sulfur dichloride. However, further sulfidation in the 6-position of the resulting sulfide proceeds concurrently to form polynuclear by-products. Moreover, sulfur dichloride takes part in the chemical equilibrium represented by the equation EQU 2SCl.sub.2 .revreaction.S.sub.2 Cl.sub.2 +Cl.sub.2
This leads to a more complicated reaction in which disulfides and other polysulfides are formed as by-products. In many cases, therefore, the end product is disadvantageously obtained in resinous form and in low yield.
Specifically, 2,2'-bis(4-tert-butylphenol)sulfide is conventionally prepared by reacting 4-tert-butylphenol with sulfur dichloride. For example, the reaction is effected in carbon tetrachloride at a temperature of from 20.degree. to 30.degree. C. However, the end product is obtained in resinous form and its identity is only approximately estimated by means of molecular weight determination (G. Katsui and H. Hisayama: Vitamin, Vol. 7, p. 145 (1954)).
Moreover, 2,2'-bis(4-tert-amylphenol)sulfide is conventionally prepared by reacting 4-tert-amylphenol with sulfur dichloride in dichloroethane. In practice, the reaction mixture is heated at reflux and then subjected to fractional distillation under reduced pressure. The resulting crude product is further purified by recrystallization to obtain an end product. However, its yield is as low as 11% (U.S. Pat. No. 2,971,940).
Furthermore, 2,2'-bis(4-methylphenol)sulfide is conventionally prepared by reacting p-cresol with sulfur dichloride in petroleum ether at room temperature. The resulting crude product is then crystallized from toluene to obtain only a 22% yield of end product (W. S. Gump and J. C. Vitucci: J. Am. Chem. Soc., Vol. 67, p. 238 (1945)).
When these prior art processes are generally applied to the preparation of 2,2'-bis(4-substituted phenol)sulfides, the reaction mixture takes a resinous form, and the resulting product not only requires a very laborious procedure for its isolation but also shows a very low yield. For such reasons, these processes cannot be regarded as economical and suitable for industrial purposes. Judging from the above-described situation of the art, it is an important technical problem to develop a process for the preparation of 2,2'-bis(4-substituted phenol)sulfides by reacting a 4-substituted phenol with sulfur dichloride in which the formation of by-products is substantially inhibited to raise the proportion of the desired product and in which the desired product can be obtained with relative ease and in good yield by subjecting the reaction mixture to common aftertreating operations.